Assembly and method for cryo-preservation of specimens in a cryogen-free environment

Abstract

A cold cryostorage assembly includes a storage chamber in which specimens can be cryo-preserved. Specimen samples are stored in a vacuum so as to minimize the risk of sample contamination. The specimen samples can be cooled and warmed at adjustable controlled rates which best suit the specimen samples in question. The storage chamber can be cooled to temperatures as low as −269° C. without the use of a cryogen that contacts the specimen sample containers. The specimens can be inserted into and / or removed from the storage chamber at individually programmed variable rates by means of an automated specimen-handling component of the assembly. The specimen handling component of the assembly can be operated by remote control, or even over the internet. The storage chamber is evacuated, and in any case, it does not involve the use of a cryogen in direct contact with sample containers in the storage chamber. The cryogen is contained inside of closed heat exchangers that are disposed in the storage chamber.

Description

[0001]This application claims the benefit of U.S. Ser. No. 60 / 548,611, filed Mar. 1, 2004.TECHNICAL FIELD[0002]This invention relates to an assembly and method for cryogenically preserving specimens at temperatures as low as 4K (−269° C.) without immersing the specimen samples directly in a liquid or a gaseous cryogen. The assembly includes a specimen insertion and retrieval system which can be operated by remote control.BACKGROUND ART[0003]Biological specimens such as blood, sperm, ova, embryos, nucleotide strands and enzymes, multi cellular specimens such as skin, and the like, are conventionally stored in racks or trays which are placed in a cryogenically cooled chamber either manually or robotically. The specimens or samples are themselves placed in ampules or vials which are then placed on the racks or trays that are immersed in the cryogenic liquid or vapor. The ampules and / or vials are typically provided with color coded dosures that can be manually coded by using an ink mark...

AI Technical Summary

Benefits of technology

[0011]This invention relates to an automated cryogenic freezer assembly; can operate at evenly distributed storage temperatures as low as 4K (−269° C.); is dependable at such low operating temperatures; can provide rapid and accurate cooling and heating between operating and ambient temperatures at controlled rates; includes a vacuum-sealed cryochamber to ensure a zero humidity storage environment; minimizes storage temperature fluctuations during specimen sample retrieval; and provides rapid access to all of the specimens in the cryochamber. The assembly also preferably includes redundant cryogen compressors for increased reliability.

[0012]The extremely low cryogenic temperatures that can be achieved in connection with this invention are accomplished by using a closed cycle thermomechanical refrigeration system that performs work on a cryogenic fluid. The system includes redundant external compressors which can compress a cryogenic fluid, and internal heat exchangers through which the cryogenic fluid is circulated. In a system that achieves the 4K operating temperature, the operative cryogenic fluid is helium. The assembly of this invention can utilize one or more cryogenic stages. By “cryogenic stages” we mean a set of cryogenic components which are at a common cryogenic temperature. A specific example of a cryogenic stage would include a cryogen expansion space that is connected to a cryo-cooler tip, which is the coldest part of the heat exchanger, and wherein the cryogen will ultimately liquefy, and a specimen sample support, which are maintained at a common cryo-temperature. In an assembly having a plurality of cryogenic stages, there could be a single primary cryogen compressor and a plurality of heat exchangers associated with that compressor. This arrangement would be useful for a single primary cryo-cooler assembly. The assembly could also be formed with redundant cryogenic stages for purposes of enhancing system reliability. The redundant stages could have their own compressors.

[0013]The cryogenic fluid undergoes a thermodynamic cycle wherein it is ultimately compressed and cooled to its liquid state, expanded back to its gaseous state, recompressed and cooled to its liquid state, so that the cycle includes alternating compression / cooling and expansion / warming of the cryogen, which in the typical system, would be the Gifford-MacMahon cycle, which is a closed loop thermodynamic cycle which makes use of valves. Coolers employing this cycle are available, inexpensive, and quite reliable. Multi staging of at least two heat exchangers would be preferred, however, the two stages can be integrated within a single cooler so that there would be negligible complexity in including the two cryogenic stages in a single cooler. By using a multistage system, the temperature of the cryogen can be lower than with a single stage cooler for the same compressor power. In order to obtain additional cooling at the 4K temperature, a Joule-Thomson expansion final stage can be added wherein the cryo fluid, helium, is pre cooled to below its inversion temperature so that expansion of the cryo fluid results in further cooling. The Gifford-MacMahon coolers would serve as precoolers in order to cool the working fluid to temperatures which are significantly below its thermodynamic inversion temperature. It may be expeditious to utilize a pulse-tube cooler with fewer moving parts instead of the Gifford-MacMahon coolers, however, for some purposes, the Gifford-MacMahon coolers are preferred for reasons of reliability and greater refrigeration capability.

Problems solved by technology

Multi staging of at least two heat exchangers would be preferred, however, the two stages can be integrated within a single cooler so that there would be negligible complexity in including the two cryogenic stages in a single cooler.

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